[sdiy] Gated VCO cycles

[john mahoney]

This isn't necessarily an answer to your question, but maybe it'll help.


> ... A gate input where the VCO is off until a gate is received, then it starts it's cycle. when the gate is turned off the VCO finishes it's cycle before going off ...

An EG with a repeat (loop) feature might do what you want. One example is Blacet's EG1:
    http://www.blacet.com/EG1.html
Says it has "Full control of Attack and Decay ramps. Gated with Semi Chaotic Release Time" in LFO mode. Um... Semi Chaotic Release Time?

Depending on the need for the LFO to finish it's last cycle, you may just need a "reset" or "sync" feature as found on, for example, the Blacet Micro LFO (on which it is actually called "Gate"):
    http://www.blacet.com
Sync/Reset is available on LFOs from most modular makers.
--
john


  ----- Original Message ----- 
  From: Peng 
  To: SDIY 
  Sent: Wednesday, January 26, 2005 12:24 PM
  Subject: [sdiy] Gated VCO cycles


  I was reading the VCO section in the EMU Modular Sythesizer Operation Manual Retrospective by Dave Rossum (lost the link, it's a PDF file) and came across an interesting feature. A gate input where the VCO is off until a gate is received, then it starts it's cycle. when the gate is turned off the VCO finishes it's cycle before going off (see page 7). I want to implement this feature in some of the VCOs I'm building, but I'm not sure how to accomplish this. Should I be looking at the switch in the VCO core?
    I'm thinking this gated on/off could solve two problems I have with my synth. One being: how to keep my LFO in time with live impro drums ? For example: I'm using a +/-5V sine to modulate cutoff on a VCF. On every key gate I would like it to modulate the frequency up before (reset). This way, if I get the lfo speed close to the drummers tempo the modulation sounds better (more locked).

    Second problem would be the sharp clicks and pops I get when playing low bass lines, especially when the waveform has low harmonic content, like a sinewave. They kinda come and go randomly with note ons and sometimes note offs. I notice this with other synths with free running oscillators and even a lot of software synths. Are these clicks/pops the result of non-zero cossings (sorry for the sample editing speak)? I can supress the clicks with EQ but that's not always desirable. 

    Any info, advice, comments,ideas are desperately needed and greatly appreciated.

  Thanks
  Peng
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